Copper base alloys and process for preparing same



United States Patent 3,475,227 COPPER BASE ALLOYS AND PROCESS FORPREPARING SAME Elmer J. Caule, New Haven, Michael J. Pryor, Hamden, andPhilip R. Sperry, North Haven, Conn., assignors to Olin MathiesonChemical Corporation, a corporation of Virginia No Drawing. Filed Oct.4, 1966, Ser. No. 584,097 Int. Cl. C23c 7/06; C22c 9/10 U.S. Cl.148-6.31 7 Claims ABSTRACT OF THE DISCLOSURE Oxidation resistant copperbase alloys and process for preparing same, with the alloys containingfrom 0.01 to 0.50% by weight of a Group V element and from 2.0 to 25.0%by weight of at least two additional elements, with the ratio of thefirst to the second of said elements being from 0.03:1 to 10:1, thefirst of said elements being either aluminum, gallium, indium orberyllium and the second of said elements being either silicon,germanium, tin or beryllium. When beryllium is the second element,aluminum is the first element.

The present invention relates to new and improved copper base alloyshaving substantially improved resistance to oxidation and tarnishing inmoist and contaminated atmospheres.

Copper base alloys have found wide and varied uses in industry andcommerce in general; however, the many useful physical properties ofthese alloys are almost invariably negated to some degree by theirextremely low resistance to oxidation and to tarnishing, especially inmoist and contaminated atmospheres. This poor oxidation and/ortarnishing resistance has limited the utility of copper base alloys andhas resulted in long and continuing eiforts to overcome thisdisadvantage.

It has long been the object of the copper industry to develop new copperbase alloys which overcome these disadvantages and are characterized bygood oxidation and/or tarnishing resistance. The copper industry hasaimed to develop new copper base alloys whose resistance to oxidationand tarnishing is at least as good as austenitic stainless steels. Theprevious approach to this problem has been the investigation of theoxidation and tarnishing characteristics of binary copper alloys wherethe binary alloying addition is strongly reducing in nature and which,by itself, grows highly protective oxidation films, for example,aluminum. This approach has been unsuccessful in attaining stainlessproperties which are self-healing in everyday environments.

There has been some limited success where the binary alloys wereprocessed in such a manner as to completely prevent the oxidation of thecopper matrix while still permitting oxidation of the alloying addition,see, for example, Journal of the Institute of Metals, 63, 21 (1938), byL. E. Price and G. T. Thomas. This result has been usually attained byselective oxidation whereby the binary alloys are subjected to hightemperature treatment in atmospheres, such as moist hydrogen, which willoxidize the reducing alloying ingredient but which maintain the copper,with its lower free energy of oxidation, in the reduced condition. Thistype of treatment often produces protective, invisible, oxide films ofthe alloying addition. These films protect the copper matrix as long asthey are not mechanically damaged. When the films are mechanicallydamaged, as they are in even mild forming operations, such asstraightening sheet, involving less than 1 percent plastic deformation,they do not repair themselves spontaneously with protective films freeof ICC copper oxide at normal temperatures or in the absence of specialatmospheres.

In U.S. Patent 3,259,491, by Michael]. Pryor, patented July 5, 1966, anoxidation resistant copper base alloy is formed by bulk alloying withcopper at least two alloying ingredients in concentration ratios to formcertain complex oxides on the surface of the alloy, i.e., the alloyingingredients are added in concentration ratios so that they diffuse tothe surface of the alloy in proportion to the concentration of theindividual alloying ingredient in the complex oxide. The above patentprovides an alloy representing a considerable advance in the art andatfording a high degree of oxidation resistance. The alloys therein areparticularly advantageous at elevated temperatures and provide extensiveoxidation resistance at, for example, 800 C. However, it is adisadvantage of these alloys that less protection is afforded over awide range of temperatures.

Co-pending application Ser. No. 436,746, now U.S. Patent 3,341,369, byElmer J. Caule, Michael I. Pryor, and Philip R. Sperry, filed Mar. 3,1965, represents an improvement over the above U.S. Patent 3,259,491.The above co-pending application attains an alloy with extensiveoxidation resistance over a wide range of temperatures.

In accordance with the teaching of said co-pending application, from 2to 25% by weight of two elements are alloyed with copper and thematerial heated in an oxidizing environment for at least one minute at atemperature of from 400 C. to the solidus temperature of the alloy. Thefirst of said two elements is selected from the group consisting of:aluminum; gallium; indium; and beryllium, the second of said twoelements is selected from the group consisting of: silicon; germanium;tin; and beryllium, provided that when beryllium is the second element,aluminum is the first element. Further, the ratio of the first to thesecond of said elements is from 0.03:1 to 10:1.

In accordance with said co-pending application this forms a firstoutside layer of copper oxides and oxides of the alloying additions 25to 5000 angstroms in depth and a second oxidation resistant layer of athickness of at least 50 angstroms immediately beneath said first layercontaining a discrete dispersion of a complex oxide ineluding at leastone of the alloying additions.

It is a finding of the above co-pending application that the first layermay be bright and shiny and oxidation resistant; however, this firstlayer could be and often is mottled or darkened in appearance. The firstlayer may, therefore, be removed to bare the second highly ennobledoxidation resistant layer which affords considerable protection to thealloy.

The present invention is related in concept to the aforementionedco-pending application and represents an improvement over saidco-pending application. In accordance with the present invention theoxidation and tarnish resistance of both the first and second layer isgreatly improved. This is particularly surprising in view of the alreadyextensive protection afforded in accordance with the above co-pendingapplication.

In accordance with the present invention it has now been found that thefirst layer actually contains two strata, with the first or outermoststratum being rich in copper oxides and the second or innermost stratum'being rich in oxides of one of the alloying elements. In accordancewith the present invention certain additional alloying elements areprovided which greatly enhance the oxidation and tarnish resistance ofthe second or innermost stratum. Furthermore, the additional alloyingelements of the present invention enhance the oxidation and tarnishresistance of the second highly oxidation resistant layer.

Accordingly, it is a principal object of the present invention toprovide a process for the preparation of new and improved copper basealloys which are capable of substantial resistance to oxidation under awide variety of conditions.

Further objects and advantages of the present invention will appearhereinafter.

In accordance with the present invention it has now been found that theforegoing objects and advantages may be readily obtained and new andimproved copper base alloys capable of substantial resistance tooxidation may be prepared.

The novel alloys of the invention may be prepared by (A) providing acopper base alloy containing from 0.01 to 0.50% by weight of a Group Velement selected from the group consisting of phosphorus, arsenic,antimony, bismuth and mixtures thereof, and from 2.0 to 25.0 percent byweight of two elements, with the ratio of the first to the second ofsaid elements being from 0.03:1 to 10:1, the first of said elementsbeing selected from the group consisting of: aluminum; gallium; indium;and beryllium, the second of said elements being selected from the groupconsisting of: silicon; germanium; tin; and beryllium, provided thatwhen beryllium is the second element, aluminum is the first element; and

(B) heating said alloy in an oxidizing environment for at least oneminute at a temperature of from 180 to 850 C. to form (1) a firstoutside layer 25 to 5000 angstroms in depth, said first layer containing(a) a first outermost stratum rich in copper oxides, and (b) a secondinnermost stratum rich in oxides of said first element, and (2) a secondoxidation resistant layer immediately beneath said first layercontaining a discrete dispersion of a complex oxide including at leastone of said two elements, said second layer being of a thickness of atleast 50 angstroms and preferably substantially greater; and (C)preferably removing the first stratum.

In the preferred embodiment an additional alloying element is provided.This may be either cobalt, cerium or iron or mixtures thereof with thetotal of these materials being provided in an amount from 0.05 to 5.0%,preferably 0.2 to 0.8%. These materials provide still greaterimprovement in properties in the present alloy.

As indicated hereinabove, from 2.0 to 25% by weight of two elements arealloyed with copper. The preferred combined amount is from 2 to 7% byweight. The relative ratio of the first to the second of said elementsmust be maintained with the following ratio, from 0.03:1 to 10:1. Thatis, the ratio of the first to the second of said elements must bemaintained within the foregoing ratio. Naturally, the ratio which ischosen for a particular system will vary widely within the foregoingbroad ratio depending upon the particular system and the relative atomicweights of the elements which are added. For example, when the twoelements are aluminum and silicon, which is preferred, the followingratio of aluminum to silicon should be employed, from 2.5 :1 to 0.5 :1.Similarly, for elements which have lower or higher atomic weights thanaluminum, the ratio should be adjusted, for example, theberyllium-silicon system utilizes the following ratio of beryllium tosilicon, 2.021 to 0.15:1. The indium-silicon system utilizes thefollowing ratio of indium to silicon, 10:1 to 02:1. The gallium-siliconsystem utilizes the following ratio of gallium to silicon, 10:1 to0.2:1. The aluminum-germanium system utilizes the following ratio ofaluminum to germanium, :1 to 02:1 and the aluminum-tin system utilizesthe following ratio of aluminum to tin, 3:1 to 0.03:1. Similarly, thefollowing ratios apply to the following systems: aluminum to beryllium,10:1 to 0.5 :1; gallium to germanium, 5:1 to 0.1:1; gallium to tin, 3:1to 01:1; indium to germanium, 10:1 to 02:1; and indium to tin, 5.021 to01:1.

It should be noted that the exact proportion of the first of saidelements to the second of said elements will be affected by the atomicweights of the respective elements, the specific complex oxides to beformed, and also the diffusion and chemical characteristics of theparticular elements.

In addition, the alloy of the present invention also contains from 0.01to 0.50% by weight of a Group V element selected from the groupconsisting of phosphorus, arsenic, antimony, bismuth and mixturesthereof, and preferably from 0.05 to 0.20% by weight. The preferredGroup V element is phosphorus.

In addition to the foregoing, it is preferred that a total from 0.05 to5% by weight of either cobalt, cerium or iron or mixtures thereof beemployed, preferably from 0.2 to 0.8% by weight, with cobalt being thepreferred additive.

Naturally, the present invention contemplates within its scope the useof other materials in combination with copper and the foregoingingredients in order to achieve particularly desired results or toprovide a particular alloy. For example, still greater oxidationresistance may be obtained by adding the following in addition to thetwo principal alloying ingredients: boron; manganese; zinc; cadmium; andberyllium where beryllium is not one of the alloying ingredients. Also,particularly desired properties may be enhanced by the addition of otheralloying ingredients while retaining oxidation resistance.

In accordance with the present invention, the particular method ofalloying copper with the chosen alloying additions is not particularlyimportant and conventional methods may be readily employed provided thatthe molten copper to which the alloying elements are added is initiallyoxygen free so that the alloying elements are not present in the alloyas oxides prior to solidification. As is conventional, the elements maybe added as master alloys or in elemental form.

It is a critical aspect of the present invention, however, that afterthe alloying additions have been added to copper, the alloy solidifiedand if desired brought into a suitable or desired product form, theresultant alloy is heated in an oxidizing environment for at least oneminute, and preferably at least five minutes, at a temperature of fromC. to 850 C., and preferably from 400 C. to 850 C. Temperatures from180-400 C. are insufiicient to form the second layer, forming only thefirst layer containing the first and second strata. Temperatures inexcess of 400 C. form both the first and second layers.

In the preferred embodiment, the alloy is heated in an I oxidizingatmosphere, such as air, to desired temperatures at a rate of at least 5C. per hour. Naturally, the particular temperature of treatment willvary depending upon the particular system and the particular resultsdesired. However, in the preferred embodiment a temperature range offrom 500 C. to 800 C. is employed. The time of holding the alloy atthese elevated temperatures should for practical purposes be less than 2days, although longer heating times may be utilized if desired. Theoptimum heating time is from one (1) hour to 10 hours.

It is critical that the alloy be heated in an oxidizing environment. Anyoxidizing environment may be readily employed, for example, preferablyair or oxygen and also molten oxidizing salt baths may be employed, suchas those containing sodium nitrate.

After the alloy has been held under the above conditions the alloy iscooled to room temperature.

The foregoing process results in an alloy having a first outside layerand a second highly oxidation resistant layer. The first outside layeris 25 to 5000 angstroms in depth and contains a first outermost stratumrich in copper oxides and a second innermost stratum rich in oxides ofsaid first element, i.e., either aluminum, gallium, indium or beryllium.The second highly oxidation resistant layer is immediately beneath thefirst layer, is at least 50 angstroms in depth and contains a discretedispersion of a complex oxide including at least one of said twoelements.

In accordance with the present invention the first layer consists of twostrata. The first or outermost stratum is predominantly copper oxides.This stratum is generally colored and provides little or no oxidation ortarnish resistance, therefore, is preferably removed. The thickness ofthis stratum will vary depending on the temperature of formation.

The second or innermost stratum of the first layer is predominantlyoxides of the first element, i.e., predominately oxides of aluminum,gallium, indium or beryllium. In accordance with the present inventionthis stratum provides considerable oxidation and tarnish resistance.This stratum is transparent, thus retaining the original luster andcolor of the substrate alloy. In accordance with Ser. No. 43 6,746,referred to above, in 1-2 months spots of discoloration appear on thesecond stratum in sufficient number to destroy the decorative utility ofa fabricated article. In accordance with the present invention, however,very few fine spots of discoloration appear on the second stratum aftera prolonged time, e.g., industrial exposures in excess of one year didnot destroy the decorative utility of the article and the article wasstill bright and shiny. This is due to the addition of the Group Velementswhich have a marked effect on the second stratum, although theyare not present in a discrete form in the second stratum. Accordingly,for practical purposes, the second stratum will provide adequateoxidation and tarnish resistance.

The copper oxides of the first stratum can be readily removed, forexample, by dissolving them away with dilute sulfuric acid solutionleaving the improved second stratum of the present invention. As pointedout above, the second stratum itself provides a high degree ofresistance to further oxidation and to outdoor tarnishing. However, ifit becomes necessary to remove the second stratum, as by pickling,bufling, etching or some mechanical forming operation, or if the secondstratum is mechanically damaged, then continued protection is alfordedby the improved second layer, which is oxidation and tarnish resistant.The Group V element effects an improvement in the second layer, althougha less marked improvement than is effected in the second stratum. Aswith the second stratum, the Group V element is not present in discreteform in the second layer.

The depth of the second layer will vary widely depending upon theparticular treatment conditions, with in all cases the thickness beingat least 50 angstroms. In general, in order to provide reasonableoxidation protection, the second layer should be a minimum of 50angstroms in depth and preferably at least 200 angstroms. The maximumdepth of the second layer is completely dependent upon the treatmentconditions and the particular system utilized, that is, longer holdingtimes and higher temperatures will provide a thicker second layer.Normally,

however, a second layer of around 2 mils is the preferred value,although for some uses it may be preferable to get a thicker secondlayer or even if desired obtain a second layer which comprises all ofthe rest of the alloy.

The second layer or highly oxidation resistant layer is characterized bycontaining a discrete dispersion of complex oxides including at leastone of said two elements. The discrete dispersion is present in themetal matrix.

In accordance with the present invention the second layer is bright andshiny in appearance and provides extensive oxidation and tarnishresistance over a wide temperature range at or below the formationtemperature range. In other words, oxidation and tarnish resistance isprovided in a bright and shiny alloy having characteristics desired inalloys of this type over a wide temperature range up to the temperatureof the heat treatment step. This second layer behaves chemically as ifit were a more noble metal than copper, i.e., it resists chemical attackby strong chemical reagents which are normally used for pickling copper.

Beneath the second layer is normally the copper base alloy itself. Thisbase would normally have only the original oxidation resistance in theabsence of the oxidation resistant layer of the present invention, butwould not have the enhanced resistance.

It is particularly surprising in accordance with the present inventionthat the addition of a group V element greatly enhances the oxidationand tarnish resistance of the second stratum, especially the tarnishresistance. Furthermore, the oxidation and tarnish resistance of thesecond layer is also improved, especially the oxidation resistance.

The cobalt, cerium or iron additions provide still further improvement.Oxidation at elevated temperature causes grain growth. The cobalt,cerium or iron additions form a fine dispersion of the additive and/orintermetallic compounds formed with them which inhibits grain growth.Thus, the alloy of the present invention contains a fine dispersion richin cobalt, cerium or iron.

The present invention and improvements resulting therefrom will be morereadily apparent from a consideration of the following illustrativeexamples.

EXAMPLE I A series of copper base alloys were prepared utilizing highpurity copper and high purity alloying additions. The alloys wereprepared by tilt mold casting into 1% x 1% x 4 inch shape, heating to1600 F. (871 C.), hot rolling in a number of passes to 0.190 inch, andcold rolling and annealing into 10 mil sheet. The resultant alloys hadthe compositions indicated in the Table I below where amounts ofingredients are percentages by weight. In all the alloys, the balancewas essentially copper.

Alloys A, B, and C, prepared in Example I, in 10 mil sheet, cold rolledform, were carefully cleaned and heated in air for two hours at varioustemperatures from 350 to 800 C. The weight gain in micrograms per squarecentimeter is shown in Table II below.

TABLE II Weight Gain in Micrograms Per Square Centimeter 350 C. 450 C.600 C. 800 C.

It is apparent that with alloys B and C film growth has virtuallystopped at a lower oxygen uptake at temperatures of 600 C. or less,i.e., those alloys with phosphorus or phosphorus and cobalt present.

EXAMPLE III spotted; alloys B and Cthere were no mottling or spotting onany of the samples and all samples were bright and shiny. Those alloy Band C samples treated at 500 C., and 450 C. showed a slight haze butwere still shiny.

EXAMPLE IV The following example demonstrates the unique character ofthe second stratum of the alloys of the present invention. Alloys A andB after the treatments of Example lI oxidized at 600 C., were dipped indilute H 80 to remove the first stratum and to bare the second stratum.The parallel resistance of a fixed area of film was measured by means ofan AC capacitance bridge. At a frequency of one kilocycle, alloy Battained a peak resistance of 80,000 ohms for a one square centimeterarea compared to only 20,000 ohms for alloy A. This demonstrates thatalloy B with the phosphorus addition has four times the electricalresistance as alloy A and is four times as good an electrical insulator.

EXAMPLE V The following example demonstrates that the alloy of thepresent invention has improved oxidation resistance in the second layer.Alloys A and B were oxidized as in Example II for two hours at 800 C.The first layer of both samples was removed, including both the firstand second stratum, by strong acid etching, removing about 5000micrograms per square centimeter for each sample. Each sample was thenreoxidized for two hours at 450 C. Alloy B registered no weight gainwithin the limits of detectability of the microbalance (approximately0.5 microgram per square centimeter), while alloy A registered a weightgain of 2 micrograms per square centimeter.

EXAMPLE VI The following example demonstrates the unique character ofthe second stratum in alloy C. Alloy C after the treatment of Example IIoxidized at 650 C., was treated as in Example IV and the parallelresistance measured as in Exmple IV. At a frequency of one kilocycle,alloy C attained a peak resistance of 103,000 ohms for a one squarecentimeter area.

EXAMPLE VH In the following example alloy C was oxidized as in ExampleII for two hours at 650 C. The first stratum was removed by sulfuricacid pickling and the second stratum was removed by means of a gaspropelled abrasive unit. The sample was exposed for several months on arooftop in an industrial atmosphere and retained its original goldenluster, with no mottling and no haze.

EXAMPLE VIII Alloys D and E, prepared in Example I, in mil sheet, coldrolled form were treated as in Example H for two hours at 800 C. Thesamples were dipped in dilute H 80, to remove the first stratum and tobare the second stratum. The resultant samples were bright and shiny.The samples were exposed for several months as in Example VII andretained their original golden luster, with no mottling and no haze.

What is claimed is:

1. A process for the preparation of a copper base alloy capable ofsubstantial resistance to oxidation which comprises:

(A) providing a copper base alloy containing from 0.01 to 0.50% byweight of a Group V element selected from the group consisting ofphosphorus, arsenic, antimony, bismuth and mixtures thereof, and from2.0 to 25.0 percent by weight of two elements, with the ratio of thefirst to the second of said elements being from 0.03:1 to 10:1, thefirst of said elements being selected from the group consisting of:aluminum; gallium; indium; and beryllium, the second of said elementsbeing selected from the group con- 8 sisting of: silicon; germanium;tin; and beryllium, provided that when beryllium is the second element,aluminum is the first element; and

(B) heating said alloy in an oxidizing environment for at least oneminute at a temperature of from to 850 C. to form (1) a first outsidelayer 25 to 5000 angstroms in depth, said first layer containing (a) afirst outermost stratum rich in copper oxides, and (b) a secondinnermost stratum rich in oxides of said first element, and (2) a secondoxidation resistant layer immediately beneath said first layercontaining a discrete dispersion of a complex oxide including at leastone of said two elements, said second layer being of a thickness of atleast 50 angstroms.

2. A process for the preparation of a copper base alloy capable ofsubstantial resistance to oxidation which comprises:

(A) providing a copper base alloy containing from 0.01 to 0.50% byweight of a Group V element selected from the group consisting ofphosphorus, arsenic, antimony, bismuth and mixtures thereof, and from2.0 to 25.0 percent by weight of two elements, with the ratio of thefirst to the second of said elements being from 0.03:1 to 10:1, thefirst of said elements being selected from the group consisting of:aluminum; gallium; indium; and beryllium, the second of said elementsbeing selected from the group consisting of: silicon; germanium; tin;and beryllium, pro vided that when beryllium is the second element,aluminum is the first element; and

(B) heating said alloy in an oxidizing environment for at least oneminute at a temperature of from 400 to 850 C. to form (1) a firstoutside layer 25 to 5000 angstroms in depth, said first layer containing(a) a first outermost stratum rich in copper oxides, and (b) a secondinnermost stratum rich in oxides of said first element, and (2) a secondoxidation resistant layer immediately beneath said first layercontaining a discrete dispersion of a complex oxide including at leastone of said two elements, said second layer being of a thickness of atleast 50 angstroms.

3. A process according to claim 2 wherein said first stratum is removed.

4. A process according to claim 2 wherein said alloy (A) contains from0.05 to 5.0% by weight of a material selected from the group consistingof cobalt, cerium, iron and mixtures thereof.

5. A copper base alloy capable of substantial resistance to oxidationcomprising:

(A) from 0.01 to 0.50% by weight of a Group V element selected from thegroup consisting of phosphorus, arsenic, antimony, bismuth and mixturesthereof, and from 2.0 to 25.0 percent by weight of two elements, withthe ratio of the first to the second of said elements being from 0.03:1to 10: 1, the first of said elements being selected from the groupconsisting of: aluminum; gallium; indium; and beryllium, the second ofsaid elements being selected from the group consisting of: silicon;germanium; tin; and beryllium, provided that when beryllium is thesecond element, aluminum is the first element; and

(B) said alloy having an inner oxidation resistant layer of a thicknessof at least 50 angstroms containing a discrete dispersion of a complexoxide including at least one of said alloying additions; and

(C) said alloy having an outer stratum less than 5000 angstroms in depthrich in oxides of said first alloying addition.

6. An alloy according to claim 5 wherein said alloy has an outermoststratum rich in copper oxides.

9 10 7. An alloy according to claim 5 including from 0.05 to 3,341,3699/1967 Caule et a1 1483 5.0% by weight of a material selected from thegroup con- 3,347,717 10/ 1967 Eichelman et a1. 75162 X sisting ofcobalt, cerium, iron and mixtures thereof. 3,366,477 1/ 1968 Eichelmanet a1. 75153 X References Cited 5 CHARLES N. LOVELL, Primary ExaminerUNITED STATES PATENTS U.S.Cl. X.R.

3,259,491 7/1966 Pryor 75162 75-153; l482, 11.5, 31.5

